1. Field of the Invention
The present invention relates generally to means for remotely opening and closing flow passages through a tubular body. More particularly, the present invention relates to means for remotely opening a subsurface flow passage in a pipe string contained within a well bore to inject fracturing slurries into the well formation.
2. Description of Prior Art Setting
After a well is drilled, it is sometimes necessary to inject pressurized fluid slurries into the well bore to fracture and prop open the resulting cracks formed in the formation. The slurry typically is made up of sand particles entrained in a supporting well treating fluid. The particulate matter lodges in the formation cracks created by the high pressure pumping to keep the cracks open after the pumping pressure is reduced. Fracturing and propping open of the formation permits an increase in the flow of the underground petroleum fluids to the well bore. The solids in the high pressure, rapidly flowing fracturing fluid can quickly erode the pipe and accessories used to pump the fluid into the formation.
Sliding sleeves are commonly employed in pipe strings to open and close subsurface access openings in the pipe as required to inject fluid into the formation or to produce fluid from the formation. An example of a prior art sliding sleeve system is shown in U.S. Pat. No. 5,263,683. The patent discloses an internal sliding sleeve within a ported pipe section. Shifting the sleeve axially so that openings in the sleeve align with openings in the pipe establishes a flow path through the wall of the pipe section. The seals above and below the pipe ports remain covered and protected by the sliding sleeve in both the open and closed positions. In this prior art device, the flow path for fluids entering or leaving the pipe extends through the pipe ports as well as the sleeve openings. The surface contours of the pipe ports and the sliding sleeve openings, as well as the annular space between the sleeve and the internal pipe wall, induce turbulent flow as the fluids traverse the flow path. The turbulent flow, in turn, when combined with entrained abrasives such as sand can quickly wear away and otherwise damage the pipe and sliding sleeve assembly.